Migration of data to sequential access medium

ABSTRACT

A computer program product for migrating data in a computer storage system. Data is selected to migrate from a first storage to the second storage, wherein selected files are in a resident state. Metadata is obtaining and subsets of data are ordered based on the obtained metadata, the order of the subsets of data following an expectation of update value. The subsets of data are transferring to the second storage based on the order of the subsets of data based on a predetermined schedule. Data determined as inactive is overwritten on the sequential access medium by transferred data. End data to the sequential access medium is set after a last active data is written before the one or more sets of data are determined to be inactive. The one or more sets of data determined to be inactive are deleted from the second storage and a transfer is initiated.

BACKGROUND

The present invention, generally, relates to storage systems, moreparticularly, to migration of data to a sequential access medium in astorage system.

A linear tape file system (LTFS) is software that allows for theperformance of standard file operations to a tape medium through a filesystem interface. Technical development of LTFS format specification isnow continued in SNIA (Storage Networking Industry Association) TWG(Technical Work Group). Several implementations of LTFS have beendeveloped for tape drives and tape libraries. Hierarchical storagesystems integrating a primary storage tier with LTFS as a secondarystorage tier have been also developed, in which part of files in theprimary storage tier is stored on tape media in the LTFS format.

Since the tape medium does not allow random access due to its sequentialnature, newly created data is always appended to the tape medium. Datadeletions just erase pointers to the data. Data updates always appendupdated data to the tape medium and just modify the pointers so as topoint the updated data. So, space on the tape medium that is occupied bydeleted or updated obsolete data may suppress capacity of the tapemedium. In the hierarchical storage systems, there is provided a processreferred as a “migration”, in which files are moved from the primarystorage tier to the tape media in the secondary storage tier. Themigration process can be scheduled at specific time, for example,off-peak hours. However, such migration process may deteriorateutilization of the tape medium due to the obsolete data on the tapemedium.

SUMMARY

It would be advantageous to have a system for migrating data to asequential access medium in a storage system, capable of improvingutilization of the sequential access medium. According to an embodimentof the present invention, there is provided a method for migrating datain a storage system by a computer system, in which the storage systemincludes a first storage and a second storage having a sequential accessmedium. The method comprises determining that the second storagecomprises an index partition and a data partition and selecting aplurality of data to migrate from the first storage to the secondstorage, wherein selected files are in a resident state. Metadataassociated with one or more subsets of data of the plurality of data isobtained. Subsets of data based on the obtained metadata are ordered,the order of the subsets of data following an expectation of updatevalue. The subsets of data are transferred to the second storage basedon the order of the subsets of data based on a predetermined schedule.It is determined that the plurality of data written in a rear region ofthe sequential access medium is inactive and the data determined asinactive is overwritten on the sequential access medium by transferreddata. The one or more sets of data written in the rear region aredetermined to be inactive and an end data to the sequential accessmedium is set after a last active data is written before the one or moresets of data are determined to be inactive. The one or more sets of datadetermined to be inactive are deleted from the second storage, and atransfer to the sequential access medium after the setting is initiated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a functional block diagram of illustrating a hierarchicalstorage system, according to an embodiment of the present invention;

FIG. 2 is a functional block diagram of illustrating a node constitutinga cluster of the hierarchical storage system, according to the anembodiment of the present invention;

FIG. 3 is a functional block diagram of illustrating a hierarchicalstorage system, according to the exemplary embodiment of the presentinvention;

FIG. 4A and FIG. 4B are flowcharts depicting a migration process withoverwriting inactive data around tail end of a tape medium according toan embodiment of the present invention;

FIG. 5A and FIG. 5B illustrate schematically the migration process withoverwriting inactive data around tail end of the tape medium, accordingto an embodiment of the present invention; and

FIG. 6 depicts a block diagram of components of the server computerexecuting an application, in according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Now, the present invention will be described using particularembodiments, and the embodiments described hereafter are understood tobe only referred as examples and are not intended to limit the scope ofthe present invention.

One or more embodiments according to the present invention are directedto methods, computer systems and computer program products for migratingdata to a sequential access medium in a storage system.

Now referring to the series of FIGS. 1-5, FIGS. 1-5 illustrate ahierarchical storage system with disk and tape tiers, and a method formigrating files to the tape medium in the hierarchical storage systemaccording to an exemplary embodiment of the present invention. First,referring to FIGS. 1-3, fundamental configurations of the hierarchicalstorage system will be described.

FIG. 1 is an overview of a hierarchical storage system according to anexemplary embodiment of the present invention. The hierarchical storagesystem 100 includes a cluster 110, a shared disk array 120, and a tapelibrary 130, and a control terminal 140 all interconnection via SANfabric 102. The cluster 110 includes one or more of node 112-1, node112-2, node 112-L, and node 112-M. Node 112-1, node 112-2, node 112-L,and node 112-M may be generally referred to as nodes 112, as seen inFIG. 1. The cluster 110 provides a file system that allows forperforming file operations to the hierarchical storage system 100.

The hierarchical storage system 100 may include a shared disk array 120that includes one or more disk cache 122-1, disk cache 122-2, and diskcache 122-N, as a primary storage tier. Disk cache 122-1, disk cache122-2, and disk cache 122-N may be referred to generally as disk caches122 as seen in FIG. 1. The shared disk array 120 may be referred simplyas the shared disk array 120. Each of nodes 112 in the cluster 110 maybe connected to the disk caches 122 in the shared disk array 120 via aSAN (Storage Area Network) fabric 102. The SAN fabric may include, butnot limited to, FC (Fibre Channel), SAN based on a fiber channel networkand/or IP (Internet Protocol), or SAN based on TCP (Transmission ControlProtocol)/IP network with LAN (Local Area Network) switches.

The nodes 112 may share the disk caches 122. The nodes 112 can accessthe disk caches 122 via the SAN fabric 102 and may provide indirect fileaccess to other nodes 112 that do not connect to the SAN fabric 102. Afile system distributed over the one or more nodes 112 in the cluster110, to which plurality of nodes (may include client nodes) can access,can be referred to as a clustered file system or a distributed parallelfile system. The clustered file system may provide a global namespace, astriping functionality to stripe input and output over the nodes and aninformation lifecycle management (ILM) functionality.

The hierarchical storage system 100 may include a tape library 130 as asecondary storage tier. The tape library 130 may be referred simply asthe tape tier. The tape library 130 includes one or more tape drives.Tape library 130 includes tape drive 132-1, tape drive 132-2, and tapedrive 132-L, which may be referred to generally as tape drives 132. Tapelibrary 130 also includes tape medium 134-1, tape medium 134-2, and134-0, which may be referred to generally as tape media 134. Any of thetape media 134 may correspond to a sequential access medium to be atarget of migration in the describing embodiment. Each of the nodes 112in the cluster 110 may be connected to the tape library 130 via SANfabric, FC LVD (Low Voltage Differential) SCSI (Small Computer SystemInterface) or SAS (Serial Attached SCSI) cables. The tape library 130may include a plurality of tape drives 132 to enable the plurality ofthe nodes 112 to access a set of the tape media 134 simultaneously. Thetape drives 132 may be occupied by one or more of nodes 112 at a pointin time and may be used alternately. The tape drives 132 acceptpreferably LTO (Linear Tape-Open) Ultrium 5 or later tape cartridges,which support LTFS.

In various embodiments, the tape library 130 may be managed by a tapefile system such as LTFS (Liner Tape File System) and integrated to theclustered file system so that at least part of data in the shared diskarray 120 is stored on tape media 134 in the tape library 130. Files maymigrate from the shared disk array 120 to the tape library 130 based ona predetermined migration policy.

The hierarchical storage system 100 may include further a controlterminal 140. The control terminal 140 is a terminal device which anadministrative user can operate, in order to issue manual request andspecify settings of the hierarchical storage system. Using the controlterminal 140, the administrative user can specify and edit the migrationpolicy for the migration process according to the exemplary embodimentof the present invention, which will be described in more detail below.The administrative user may issue a manual request and specify schedulesor policies for other functionalities of the hierarchical storage system100, such as standard migration, recall, reclamation, reconciliation,file placement, file management, etc.

In various embodiments, the hierarchical storage system 100 isintegrated with LTFS systems and applications that are adapted foraccessing hard disk drives may be used directly without modifying theapplication. Since the system accesses files first on the shared diskarray 120 instead of directly accessing files on the tape media 134,time-out to access a file may be avoided.

In various embodiments, the nodes 112-1-112-M are described to beconnected to the disk caches 122-1-122-N in the shared disk array 120and the nodes 112-1-112-L are described to be connected to the tapedrives 132-1-132-L in the tape library 130. It should be appreciatedthat the configuration of the hierarchical storage system 100 describedabove in reference to FIG. 1 is only exemplary of a typical storagesystem and is not intended to suggest any limitation.

In an embodiment, the shared disk array may be divided into one or moreonline storage tiers and one or more near line storage tiers toconstruct a three or more tiered architecture. In another embodiment,the hierarchical storage system may include further a flash storage tieron top of the disk tier or in place of the disk tier. In an additionalembodiment, the storage system may have merely one node, one disk cacheand one tape drive to construct a hierarchical storage system. In anadditional embodiment, another type of a sequential access medium may beused as a target of the migration in place of or in addition to the tapemedium.

Referring to FIG. 2, FIG. 2 is a schematic of an example of a nodeaccording to an embodiment of the present invention. The nodes 112 areonly one example of suitable nodes and are not intended to suggest anylimitation as to the scope of use or functionality of embodiments of theinvention described herein. The nodes 112 are capable of beingimplemented and/or performing any of the functionality set forth herein.

The nodes 112 are operational with numerous other general purpose orspecial purpose computing system environments or configurations.Examples of well-known computing systems, environments, and/orconfigurations that may be suitable for use with the nodes 112 include,but are not limited to, personal computer systems, server computersystems, thin clients, thick clients, hand-held or laptop devices,multiprocessor systems, microprocessor-based systems, set top boxes,programmable consumer electronics, network PCs, minicomputer systems,mainframe computer systems, and distributed cloud computing environmentsthat include any of the above systems, or devices.

The nodes 112 may be described in the general context of computersystem-executable instructions, such as program modules, being executedby a computer system. Generally, program modules may include routines,programs, objects, components, logic, data structures, and so on thatperform particular tasks or implement particular abstract data types.

Referring to FIG. 2, the nodes 112 are shown in the form of ageneral-purpose computing devices. The components of the nodes 112 arediscussed in more detail in reference to FIG. 6, and may include, butare not limited to, one or more processors (or processing units) 10 amemory 12, storage device 14, network adapter 16, and interface 18,operatively coupled to the processors by a bus including a memory bus ormemory controller, and a processor or local bus using any of a varietyof bus architectures.

The nodes 112 typically include a variety of computer system readablemedia. Such media may be any available media that is accessible by thenodes 112, and include both volatile and non-volatile media, removableand non-removable media.

Referring to FIG. 2, the memory 12 can include computer system readablemedia in the form of volatile memory, such as random access memory (RAM)604. The nodes 112 may further include other removable/non-removable,volatile/non-volatile computer system storage media. By way of exampleonly, the storage device 14 can be provided for reading from and writingto a non-removable, non-volatile magnetic media. A magnetic disk drivefor reading from and writing to a removable, non-volatile magnetic disk(e.g., a “floppy disk”), and an optical disk drive for reading from orwriting to a removable, non-volatile optical disk such as a CD-ROM,DVD-ROM or other portable computer readable storage media can beprovided. In such instances, each can be connected to bus by one or moredata media interfaces. As will be further depicted and described below,the storage device 14 may include at least one program product having aset (e.g., at least one) of program modules that are configured to carryout the functions of embodiments of the invention.

Programs may be stored in the storage device 14 by way of example, andnot limitation, as well as an operating system, one or more additionalapplication programs, other program modules, and program data. Each ofthe operating system, one or more additional application programs, otherprogram modules, and program data or some combination thereof, mayinclude an implementation of a networking environment. Program modulesgenerally carry out the functions and/or methodologies of embodiments ofthe invention as described herein.

The nodes 112 may also communicate with one or more peripherals such asa keyboard, a pointing device, a display, or one or more devices thatenable a user to interact with the nodes 112; and/or any devices thatenable the nodes 112 to communicate with one or more other computingdevices via SAN fabric 102. Such communication can occur viaInput/Output (I/O) interfaces 18. Still yet, the node 112 cancommunicate with one or more networks such as a local area network (LAN)104, a general wide area network (WAN), and/or a public network (e.g.,the Internet) via the network adapter 16. As depicted, the networkadapter 16 communicates with the other components of the node 112 viabus. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with the node112. Examples, include, but are not limited to: microcode, devicedrivers, redundant processing units, external disk drive arrays, RAIDsystems, tape drives, and data archival storage systems, etc. The nodes112 may be interconnected with other node via a host channel adapter(HCA) such as InfiniBand™.

LAN 104 may include permanent connections, such as wire or fiber opticcables, or temporary connections made through telephone or wirelesscommunications. LAN 104 may represent a worldwide collection of networksand gateways, such as the Internet, that use various protocols tocommunicate with one another, such as Lightweight Directory AccessProtocol (LDAP), Transport Control Protocol/Internet Protocol (TCP/IP),Hypertext Transport Protocol (HTTP), Wireless Application Protocol(WAP), etc. LAN 104 may also include a number of different types ofnetworks, such as, for example, an intranet, a local area network (LAN),or a wide area network (WAN).

Hardware and/or software components of the tape library 130, the tapedrives 132, and the control terminal 140 may include, similar to thenodes 112 shown in FIG. 2, a processer, a memory, a read only memory, anetwork adopter, and a I/O interface, but not be shown in the drawingsany more.

Referring to FIG. 3, FIG. 3 is a block diagram of the hierarchicalstorage system 100, according to an embodiment of the present invention.The hierarchical storage system 100 includes a computer system 200connected to the shared disk array 120 and the tape library 130. Thecomputer system 200 may be composed of the nodes 112 shown in FIGS. 1and 2.

The computer system 200 may include a clustered file system module 210,a storage management module 220, a scheduled migration module 230, and atape file system module 240. The clustered file system module 210 may bea software component that manages the clustered file system(corresponding to the shared disk array 120) in the hierarchical storagesystem 100.

The storage management module 220 may be a software component thatprovides integration of the clustered file system managed by theclustered file system module 210 with the tape file system managed bythe tape file system module 240. The storage management module 220manages standard migration and recall activities in the hierarchicalstorage system 100.

The tape file system module 240 may be a software component that allowsfor performing file operations to the tape media and providing interfaceto manipulate files on the tape media in the tape library 130. The tapefile system module 240 accesses recording space on the tape mediathrough their file system interface and handles data as file objects andassociated metadata. The tape library 130 may be mounted entirely as afile system, and the tape media 134 in the tape library 130 may beaccessed as subdirectories under a mount point of the tape library 130.

In various embodiments of the invention, migration, recall, andreconciliation in the hierarchical storage may be utilized by thesystem. Migration is a process in which files are moved from the shareddisk array 120 to the tape media 134 on the tape library 130. Themigration process may have plurality of modes. In a first mode, themigration process leaves behind a small stub file on the shared diskarray 120, which points the file body migrated to the tape medium. Themigration process in a second mode is so-called as a pre-migration, inwhich files are moved from the shared disk array 120 to the tape media134 on the tape library 130 without replacing the file body with a stubfile on the shared disk array 120. According to the pre-migration,identical copies of the files are on both the disk and tape tiers.Recall is a process in which the migrated files are moved from the tapemedia back to the originating disk tier if an accessed file does notexist on the shared disk array 120.

The files newly created or overwritten to the hierarchical storagesystem 100 may initially be merely on the shared disk array 120, thusthe file state is initially “resident”. The files may be migrated fromthe shared disk array 120 to the tape library 130 by migration process,after which the file is a stub on the disk and the identifiers of thetapes storing the copies are written to metadata. The file state of suchfile is referred as “migrated”. The file may be recalled from the tapelibrary 130 by recall activities when an application attempts to readfrom the file. The file state of such file on both the disk and tapetiers is referred as “pre-migrated”. Also the files may be pre-migratedto the tape library 130 by running the migration process in second mode.

In the hierarchical storage system according to a particular embodiment,deletions or updates of file just delete or update the file on theshared disk array 120, and such operations may not be reflected to thetape media 134 on the tape library 130. Thus, obsolete data that isdeleted or updated may still remain on the tape media. Reconciliation isa process in which the shared disk array 120 is synchronized withcontents of the tape media 134 and old and obsolete data are deletedfrom the tape media 134. These obsolete objects can be identified asinactive after the reconciliation process. However, note that theinactive objects still occupy recording space on the tape media 134. Thereconciliation process may be executed when files in the d shared diskarray 120 are deleted, moved, or renamed.

The migration process can be triggered by using predetermined migrationpolicy. The migration policy may include thresholds for utilization ofthe tape medium to start the migration process and/or to end themigration process. For examples, a policy may start the migrationprocess when a specific pool reaches 80% capacity and continuesmigration until the pool is reduced to 60% capacity or less. Themigration policy also can include a timing condition in which themigration process is scheduled at specific time such as off-peak hours.

However, such migration process may deteriorate the utilization of thetape medium due to following reason: Even though recently created orupdated fresh files empirically tend to be updated again, however, theprocess migrates all files regardless of whether the file is fresh ornot. The files that are migrated just after being created or updatedlikely become inactive. Such recording space occupied by inactive filesmay suppress capacity of the tape medium. Nonetheless, the amount ofsuch inactive files on the tape medium tends to increase as themigration processes repeated. So, there is room for improvement in themigration process to the tape medium.

Therefore, it may be advantageous to have a computer systems or computerprogram products for migrating data to a tape medium in the hierarchicalstorage system, capable of improving utilization of the tape medium. Invarious embodiments of the present invention, a migration function maybe incorporated into the hierarchical storage system 100. A process ofthe migration function may be triggered in response to determining thata predetermined timing condition is met. During the migration process,the computer system 200 selects a plurality of files to migrate from theshared disk array 120 to the tape library 130. The computer system 200obtains metadata information of each file and orders the plurality ofthe files based on the obtained metadata information. The metadatainformation may suggest the expectation of a corresponding file to beupdated. Thus, the order of the files can follow the expectation of theupdate of the files. The computer system 200 transfers the plurality ofthe files to the tape library 130 based on the order of the files.

Before substantial transfer for each tape medium occurs, the computersystem 200 determines whether data written in a rear region of the tapemedium (around end of data (EOD)) is active or inactive. If the data isdetermined to be inactive, the computer system 200 overwrites the datain the rear region by migrated data.

In various embodiments of the present invention, the order of the filesmigrated to the tape library 130 may be determined based on the metadatainformation of the files. The files that are expected to become inactivebefore next migration process on the basis of the metadata informationmay be concentrated around end of the tape media 134. The file that hasbecome inactive after the previous migration process may be overwrittenby migrated data and a space occupied by the inactive data may be reusedduring a next migration process, and may improve the efficacy of tapemedium utilization. The utilization may be measured as a percentage orratio of valid capacity for the valid files to the total tape capacityof the tape medium.

In an exemplary embodiment, the computer system 200 includes further ascheduled migration module 230. Hereinafter, the migration functionaccording to the exemplary embodiment of the present invention will bedescribed in detail with referring FIGS. 3, 4, and 5.

The scheduled migration module 230 may be a software component thatprovides the migration function according to the exemplary embodiment ofthe present invention. The scheduled migration module 230 is configuredto perform the migration process in response to satisfying thepredetermined timing condition. As shown in FIG. 3, the scheduledmigration module 230 may include a file selection and orderingsub-module 232 and a file transfer and overwriting sub-module 234.

In an embodiment of the invention, the file selection and orderingsub-module 232 is configured to select a plurality of files to bemigrated and obtain metadata information of each selected file. The fileselection and ordering sub-module 232 is further configured to performordering of the selected files based on the metadata information. In apreferable embodiment, the plurality of the selected files may beordered such that the order gets lower (i.e. migrates later) as theexpectation of the update increases. The expectation of the update ofthe file can be measured by the metadata information, which includes atimestamp, a name, an extension, size or combination thereof.

For example, recently created or updated files may be updated again,since such file can be a document in progress. Files with a specificstring such as “log” or files with an extension that is used for logfiles such as “.log” also empirically tend to be updated again, sincesuch log file may be update frequently or regularly. Files havingsmaller size expected to be updated more frequently than the fileshaving larger size.

The file transfer and overwriting sub-module 234 is configured totransfer the ordered files from the shared disk array 120 to the tapelibrary 130 based on the order of the files. The file transfer andoverwriting sub-module 234 is further configured to determine whetherdata written in a rear region of the tape media 134 is inactive beforestarting a substantial transfer processing for the tape media 134. Thefile transfer and overwriting sub-module 234 is further configured tooverwrite the data on the tape media 134 by transferred data during themigration process if the data is determined to be inactive.

To overwrite the inactive data on the tape media 134, the file transferand overwriting sub-module 234 sets end of data (EOD) to the tape media134 after last active data on the tape medium 134 and initiates transferto the tape media 134 after the EOD is set.

In various embodiments, the hierarchical storage system 100 includes oneor more modules to provide various features and functions. These modulesmay be implemented in hardware, software or firmware executable onhardware, or a combination thereof. Also, these modules are presentedonly by way of example and are not intended to suggest any limitation.Alternative embodiments may include additional or fewer modules thanthose illustrated in FIG. 3, or the modules may be organizeddifferently. Furthermore, it should be appreciated that, in someembodiments, the functionality of some modules may be broken intomultiple modules or, conversely, the functionality of several modulesmay be combined into a single or fewer modules.

In reference to FIGS. 4 and 5, the migration process with overwritinginactive data around tail end of the tape medium is illustrated. FIG. 4Ais a flowchart of a main routine of the migration process and FIG. 4B isa flowchart of a subroutine for each tape medium. FIG. 5 illustrates themigration process with overwriting inactive data around tail end of thetape medium. Note the tail end of the tape medium can be defined by endof data (EOD) of the tape media 134 in LTFS format.

In reference to FIG. 4A, process begins at step S100. Note that theprocess shown in FIG. 4A may be performed by the nodes 112 allocated tomanage the migration process in response to satisfying the predeterminedtiming condition. The destination of the migration may be specified as apool of the tape media 134 in the tape library 130 or a single tapemedia 134. The tape drives 132 to be used for the migration or thenumber of the tape drives 132 to be used for the migration may bespecified from among currently available tape drives 132.

At step S101, the nodes 112 select a plurality of files to migrate fromthe shared disk array 120 to the tape library 130 by the file selectionand ordering sub-module 232. In a particular embodiment, files with a“resident” state may be selected as targets of the migration. At stepS102, the nodes 112 obtain metadata information of each selected file,such as node information in the clustered file system, by the fileselection and ordering sub-module 232. At step S103, the nodes 112 orderthe selected files based on the metadata information by the fileselection and ordering sub-module 232. A set of target files, F={f1, . .. , fn}, is prepared, in which the target files fi (i=1, . . . , n; n isthe number of files selected) are sorted based on the metadatainformation.

In an embodiment, the metadata information may be a timestamp on updateand the target files may be sorted in an ascending order starting fromthe least recently updated file, for example. In various embodiments,the metadata information may be the name, the extension, or the size, inplace of or in addition to the timestamp.

At step S104, the nodes 112 control to mount each tape medium from amongthe specified pool onto each tape drive 132. To minimize the total timerequired for the migration, the system may mount tape media 134 on allavailable tape drives 132 in the system 100 to migrate multiple files inparallel.

Migration using the plurality of the tape drives 132 makes it possibleto shorten the time required for the migration. Following advantages maybe achieved in terms of user's operations: When the migration isscheduled at the time specified by the user such as night or any otherperiod of time during which the primary shared disk array 120 is notused, occurrence of a case where the migration fails to be completeduntil desired timing such as morning can be preferably prevented.

At step 105, the nodes 112 migrate the ordered files, fi (i=1, . . . ,n) to the mounted tape media 134 based on the order of the selectedfiles by file transfer and overwriting sub-module 234. In a particularembodiment, the ordered files, fi (i=1, . . . , n) may be migrated in anascending order starting from the least recently updated file.

At step S106, the nodes 112 determine whether the migration process iscompleted. For example, when all selected files are migrated to the tapelibrary 130, the nodes 112 determine that the migration process isfinished. If the nodes 112 determine that the migration process is notfinished, in step S106 “NO” branch, then the process loops back to stepS104 so as to mount other remaining tape media onto the tape drives. Ifthe nodes 112 determine that the migration process is finished, in stepS106 “YES” branch, then the process proceeds to step S107 and ends atstep S107. In this manner, the files with a recent update timestamp arearranged in a rear region of last tape media.

Referring to FIG. 4B, the subroutine begins at step S200 by initiatingthe migration processing for each tape medium at the step S105 shown inFIG. 4A. Note that the process shown in FIG. 4B may be performed by thenodes 112 allocated to handle the substantial migration processing forthe particular tape medium.

At step S201, the nodes 112 determine whether a rearmost file on thetape media 134 is inactive. In accordance with the LTFS specification, atape medium that includes an index partition and a data partition isrequired. The index partition contains index data such as informationassociated with allocation of files. The data partition contains all ofcontent data and the index data. When the file is deleted from the tapemedium, the system erases pointers to corresponding content data in theindex data. Thus, the nodes 112 can determine whether the file on thetape medium is inactive or not by referring the index data of the tapemedium.

In the hierarchical storage system according to an embodiment, the tapefile system module 240 is not notified upon moves, renames, or deletionsof files in the shared disk array 120. Therefore, the metadata of themigrated files on the shared disk array 120 may diverge from theirequivalents on tape library 130. The reconciliation process is providedto synchronize the shared disk array 120 with the tape media and todelete old and obsolete data from the tape medium. Therefore, thereconciliation process can be performed before the migration process sothat these obsolete objects are deleted from the tape medium andidentified as inactive.

However, this is only an example of ways for identifying inactive datain the hierarchical storage system 100, and is not intended to suggestany limitation. In various embodiments, the tape file system module 240may be notified from the clustered file system module 210 so as toreflect operations, which are issued to the shared disk array 120, intothe tape media 134 on the tape library 130 in real time. The index datais read from the index partition of the tape media 134 to the diskcaches 122 or memory device at the time of mounting of the tape media134. Therefore, the system can flag on the index data in the disk caches122 or the memory device such that the obsolete objects can beidentified as inactive in real time and deleted from the tape media 134at the time of mounting of the tape media 134. Note that the inactiveobjects still occupy recording space on the tape medium.

If the nodes 112 determines that the rearmost file is inactive indecision step S201 “YES” branch, the process branches to step S202. Atstep S202, the nodes 112 writes end of data (EOD) just after a lastactive file and the process proceeds directly to step S207. At stepS207, the nodes 112 starts to migrate the files to the tape media 134,and ends at step S208.

Referring to FIG. 5A, in various embodiments, several files around thetail end of the tape medium are overwritten if these files on the tapemedium become inactive before the current migration process. In FIGS. 5Aand 5B, recording space of the tape media 134 is depicted by arectangular band 500 a and rectangular band 500 b, generally designatedas bands 500. The left hand side of each of bands 500 may correspond tofront side of the recording space whereas the right hand side of each ofbands 500 may correspond to the rear side of the recording space. Thefile object is depicted by file 1 of band 500 a and file 1 of band 500b, in the bands 500. The white box, file 1 of band 500 b, represents anactive object whereas a gray box, for example, the file generallydesignated as File 8 in band 500 b of FIG. 5A represents an inactiveobject. In FIG. 5A, the upper band 500 a represents recording space justafter the previous migration process is completed. The lower band 500 brepresents the recording space just before the current migration processis started.

Referring to FIGS. 4B and 5A, the last three files (file 6, file 7 andfile 8) are active at the time of the previous migration process (seethe upper band 500 a in FIG. 5A). However, these three files becomeinactive before the current migration process due to deletion of filesfrom and/or update of files in the hierarchical storage system 100 afterthe previous migration process, for example (see the lower band 500 b inFIG. 5A). In an embodiment, the nodes 112 set the EOD to the tape media134 just after last active file (file 5) is written before the rearmostfile that is determined to be inactive (file 6), at step S202. The spacethat is occupied by these inactive files, from a file just after thelast active file to the file determined to be inactive (e.g. from file 6to file 8), is overwritten when the migration to the tape media 134starts at step S207 for the current migration process.

If the nodes 112 determines that the rearmost file is active in decisionstep S201 “NO” branch (FIG. 4B), the process branches to step S203. Atstep S203, the nodes 112 determine whether there is any inactive filenear the rearmost file. If the nodes 112 determine that there is atleast an inactive file near the rearmost file, in decision step S203“YES” branch, the process branches to step S204. At step S204, the nodes112 save the active rearmost file to the disk caches 122 or the memorydevice to make the file inactive. At step S205, the nodes 112 write theEOD on the tape media 134 just after the last active file, which is notthe saved rearmost file. At step S206, the nodes 112 move the saved filein the disk caches 122, or the memory device, back to the tape media 134and the process proceeds to step S207. At step S207, the nodes 112 startto migrate the files to the tape media 134, and ends at step S208.

Referring to FIG. 5B, several files on the tape media 134 areoverwritten when the rearmost file on the tape medium is still activebut the next files to the rearmost file on the tape medium becomeinactive before the current migration process. In FIG. 5B, the firstband 510 a represents recording space just after the previous migrationprocess is completed. The second band 510 b represents recording spacejust before the current migration process is started. The third band 510c represents recording space just after the rearmost file is saved andbecomes inactive. Bands 510 a, 510 b, and 510 c may be generallydesignated as bands 510.

As shown FIG. 5B, the last three files of band 510 a (file 6, file 7 andfile 8) are active at the time of the previous migration process. Someof these files (file 6 and file 7 in describing example) become inactivebefore the current migration process, represented in FIG. 5B as shadedfile 6, and file 7. However, some of these files, for example, file 8,still remains as active at the time of the current migration processrepresented by band 510 b.

Referring to FIGS. 4B and 5B, after saving the active rearmost files tothe disk caches 122 or the memory device, the nodes 112 set the EOD tothe tape medium just after the last active file, file 5 in band 510 b,which is not the active rearmost file. The space occupied by these filesincluding the rearmost file, file 8 of band 510 b, is overwritten whenthe migration to the tape media 134 starts at step S207 for the currentmigration process. The saved rearmost file, saved file 514, which maybe, in various embodiments, file 8, may be moved back to the currenttape media 134 before starting the migration process, in band 510 c. Byrepeating the above described saving and moving steps, the rear regionoccupied by inactive files between active files can be efficientlyoverwritten for reused.

In various embodiments, the range of rear region where the nodes 112inspect, to determine whether there is any inactive data or not, can belimited using a predetermined threshold. The saving and the moving areperformed merely if the time estimated for saving and/or moving anactive file or active files does not exceeds the predeterminedthreshold.

Referring back to FIG. 4B, in decision step S203, if the nodes 112determine that there is no inactive data near the rearmost file indecision step S203 “NO” branch, the process branches to step S207,directly. At step S207, the nodes 112 start to migrate the files to thetape media 134 without overwriting data around the end tail of the tapemedium, and ends at step S208.

In an embodiment, the rearmost file saved into the disk caches 122 ismoved back to the originating tape medium. In additional embodiments,the nodes 112 can move the rearmost file to other tape medium. Therearmost file may be saved into the disk caches 122, or memory device,and move to the other tape medium from the disk cache 122.Alternatively, the rearmost file may be moved directly from theoriginating tape medium to the other tape medium.

Referring back to FIG. 5B, in various embodiments, the rearmost file 514is moved to other tape medium. In FIG. 5B, the fourth band 510 drepresents recording space of the other tape medium. As shown in FIG.5B, the saved rearmost file 514 may be moved to a tape medium other thanthe current tape media 134 before starting the migration process in band510 d. The migration process overwriting inactive data around the endtail of the tape medium can be applicable to both modes of the migrationprocess. In an embodiment, the migration process is performed in thefirst mode, in which a target file is moved from the shared disk array120 to the tape media 134 of the tape library 130 and a stub is left onthe shared disk array 120 in place of the target file. Thus, the filestate of the migrated file becomes “migrated”. In additionalembodiments, the migration process is performed in the second mode, inwhich a target file is copied from the shared disk array 120 to the tapemedia 134 of the tape library 130 such that identical copies of thetarget file exist on the shared disk array 120 and the tape library 130.The file state of these migrated file becomes “pre-migrated”.

Referring back to FIGS. 4A and 4B, in an embodiment of the invention,steps S101-S103, step S105, and steps S201-S207, may be performed everymigration process. In various embodiments, the steps of determining andoverwriting (steps from S201 to S206) can be omitted for at least firstmigration process. The steps of obtaining (step S102) and ordering (stepS103) can be omitted if user does not plan to perform the migrationprocess.

According to the migration function described in FIGS. 5A and 5B, theorder of the files migrated to the tape library 130 is determined on thebasis of the metadata information, such that the files expected tobecome inactive before next migration process are arranged in the rearregion around the end of the tape media 134. The file that becomesinactive after the previous migration process would be overwritten bymigrated data, and a space occupied by the inactive data can be reusedduring a next migration process. The inactive recording space around thetail end of the tape medium may be reduced efficiently, and may improveutilization of the tape medium.

Referring to FIG. 6, FIG. 6 depicts a block diagram of components of thenodes 112, in accordance with an embodiment of the present invention. Itshould be appreciated that FIG. 6 provides only an illustration of oneimplementation and does not imply any limitations with regard to theenvironments in which different embodiments may be implemented. Manymodifications to the depicted environment may be made.

The nodes 112 may include one or more processors 602, one or morecomputer-readable RAMs 604, one or more computer-readable ROMs 606, oneor more computer readable storage media 608, device drivers 612,read/write drive or interface 614, network adapter or interface 616, allinterconnected over a communications fabric 618. Communications fabric618 may be implemented with any architecture designed for passing dataand/or control information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system.

One or more operating systems 610, and one or more application programs611, are stored on one or more of the computer readable storage media608 for execution by one or more of the processors 602 via one or moreof the respective RAMs 604 (which typically include cache memory). Inthe illustrated embodiment, each of the computer readable storage media608 may be a magnetic disk storage device of an internal hard drive,CD-ROM, DVD, memory stick, magnetic tape, magnetic disk, optical disk, asemiconductor storage device such as RAM, ROM, EPROM, flash memory orany other computer-readable tangible storage device that can store acomputer program and digital information.

The nodes 112 may also include a R/W drive or interface 614 to read fromand write to one or more portable computer readable storage media 626.Application programs 611 on the nodes 112 may be stored on one or moreof the portable computer readable storage media 626, read via therespective R/W drive or interface 614 and loaded into the respectivecomputer readable storage media 608.

The nodes 112 may also include a network adapter or interface 616, suchas a TCP/IP adapter card or wireless communication adapter (such as a 4Gwireless communication adapter using OFDMA technology) for connection toa network 617. Application programs 611 on the nodes 112 may bedownloaded to the computing device from an external computer or externalstorage device via a network (for example, the Internet, a local areanetwork or other wide area network or wireless network) and networkadapter or interface 616. From the network adapter or interface 616, theprograms may be loaded onto computer readable storage media 608. Thenetwork may comprise copper wires, optical fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers.

The nodes 112 may also include a display screen 620, a keyboard orkeypad 622, and a computer mouse or touchpad 624. Device drivers 612interface to display screen 620 for imaging, to keyboard or keypad 622,to computer mouse or touchpad 624, and/or to display screen 620 forpressure sensing of alphanumeric character entry and user selections.The device drivers 612, R/W drive or interface 614 and network adapteror interface 616 may comprise hardware and software (stored on computerreadable storage media 608 and/or ROM 606).

The present invention may be a computer system, a method, and/or acomputer program product. The computer program product may include acomputer readable storage medium (or media) having computer readableprogram instructions thereon for causing a processor to carry outaspects of the present invention.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

Based on the foregoing, a computer system, method, and computer programproduct have been disclosed. However, numerous modifications andsubstitutions can be made without deviating from the scope of thepresent invention. Therefore, the present invention has been disclosedby way of example and not limitation.

What is claimed is:
 1. A computer program product for migrating data ina storage system by a computer, the storage system including a firststorage and a second storage having a sequential access medium, thecomputer program product comprising: one or more computer-readablestorage media and program instructions stored on the one or morecomputer-readable storage media, the program instructions comprising: inresponse to instructions to determine that the second storage comprisesan index partition and a data partition, instructions to select aplurality of data to migrate from the first storage to the secondstorage, wherein selected files are in a resident state; instructions toobtain metadata associated with one or more subsets of data of theplurality of data; instructions to order the subsets of data based onthe obtained metadata, the order of the subsets of data following anexpectation of update value; instructions to transfer the subsets ofdata to the second storage based on the order of the subsets of databased on a predetermined schedule; in response to instructions todetermine the plurality of data written in a rear region of thesequential access medium being inactive, instructions to overwrite thedata determined as inactive on the sequential access medium bytransferred data; in response to instructions to determine that the oneor more sets of data written in the rear region are inactive,instructions to set an end data to the sequential access medium after alast active data is written before the one or more sets of data aredetermined to be inactive; instructions to delete the one or more setsof data determined to be inactive from the second storage; instructionsto initiate a transfer to the sequential access medium after thesetting.